Genetic diagnostics for use in the analysis of DNA in biological samples are promising new preventive and diagnostic methods for various diseases. The following techniques have been proposed as techniques that can analyze DNA in a simple and accurate manner.
A method for analyzing DNA is known that comprises the steps of hybridizing an analyte DNA with a DNA probe that has a base sequence complementary to the analyte DNA and is labeled with a fluorescent substance, and detecting a fluorescent signal generated upon the hybridization (see, for example, JP H7 (1995)-107999A (PLT 1) and JP H11 (1999)-315095A (PLT 2)). In this method, the formation of double stranded DNA by the hybridization is detected by fluorescence of a dye.
A method is also known that comprises hybridizing a gene sample modified to a single strand with a single stranded nucleic acid probe complementary thereto, then adding a double stranded recognition substance such as an intercalator, and performing electrochemical detection (see, for example, JP 2573443B (PLT 3) and Hyomen Kagaku (Surface Science) Vol. 24, No. 11. pp. 671-676, 2003 (NPL 1)).
On the other hand, in recent years, damage to genital systems, nervous systems and the like by exogenous endocrine disrupting chemicals (environmental hormones) including dioxins is recognized as social problems. At the present time, various methods are used to detect exogenous endocrine disrupting toxicity. Such chemicals exhibit toxicity at a very low concentration on a level of approximately 10 ppt. Accordingly, the development of a method for detecting exogenous endocrine disrupting chemicals in a low concentration range has been desired.
In particular, exogenous endocrine disrupting chemicals are bound to target DNA through a protein such as a receptor and so that it influences the expression of the DNA, whereby toxicity is produced. That is, the exogenous endocrine disrupting chemicals are bound indirectly to DNA through a protein such as a receptor rather than direct binding to DNA. Accordingly, in conventional methods such as pre-screening using DNA bindability, the evaluation of the binding is not easy.
Solar batteries are known for generating electric energy from light using sensitizing dyes (see, for example, JP H1 (1989)-220380A (PLT 4)). Solar batteries comprise a polycrystalline metal oxide semiconductor and a layer of a sensitizing dye provided in a wide range of the surface area of the semiconductor.
Further, a proposal of utilizing photocurrent generated by the photoexcitation of dyes in the detection of analytes (biological molecules such as DNAs and proteins) has been made as an attempt to apply the properties of such solar batteries in biochemical analyses (see, for example, JP 2002-181777A (PLT 5)). An improvement in measurement accuracy has been still demanded in methods for detecting analytes utilizing photocurrent generated by the photoexcitation of such dyes. As long as the present inventors know, specifying the cause of the so-called noise current and eliminating an influence of the noise current with high efficiency have been demanded.
A gene detection apparatus for determining the presence of a target gene to be detected is also known. In the use of the gene detection apparatus, a single stranded nucleic acid probe having a base sequence complementary to the target gene is immobilized on a surface of an electrode, the probe is reacted with an analyte containing a gene modified to a single strand, a double stranded recognition material is then bound to the nucleic acid probe hybridized with the gene, and the bound product is detected by electrochemical measurement to determine the presence of the target gene (see, for example, JP 2000-83647A (PLT 6)). The electrochemical measurement is carried out by immersing a working electrode and a counter electrode in an electrolysis solution and measuring oxidation current by linear sweep voltammetry. This method can realize the detection of an analyte with high accuracy. In this case, the spot for capturing the analyte in the working electrode should be single. Accordingly, a method that can realize highly efficient measurement of a plurality of samples has been still demanded.